This invention relates to a diesel engine, and more particularly to an improved combustion system for an open chamber diesel engine, which produces a controlled burning rate of the fuel during combustion and the expansion stroke of the engine to produce good engine performance with low gaseous emissions.
As is well known, increasing concern over air pollution has resulted in controls over the gaseous emissions of internal combustion engines, both at the Federal and State levels. The State of California already has emission regulations for diesel engines, which will apply to new machines in the 1973 model year, plus more stringent standards which will apply to 1975 or later model year machines. It is considered quite likely that other states will adopt similar regulations.
The 1973 California regulations specify that the exhaust emissions shall not exceed 16 grams hydrocarbons plus oxides of nitrogen or 40 grams carbon monoxide per brake horsepower hour, when the engine is run under a standard procedure. The 1975 regulations reduce the hydrocarbons plus oxides of nitrogen to 5 grams and the carbon monoxide to 25 grams per brake horsepower hour. While the carbon monoxide limits are not difficult to meet, the hydrocarbons plus oxides of nitrogen standard will present a problem, which arises, not because of the unburned hydrocarbons, which can be controlled, but as a result of the oxides of nitrogen. While the 1973 standards will not present a problem for most commercially available diesel engines, the 1975 standards will, since, according to the data available, the level of oxides of nitrogen emission in most diesel engines is such that the 1975 standards cannot be met with said engines.
While the mechanics of the production of oxides of nitrogen in the combustion process are not completely known, it is believed that such oxides are formed as the result of the breakdown of the N.sub.2 molecules in the combustion air as a result of high combustion temperatures.
Concurrent with the increased concern over exhaust emissions, there has been a trend toward higher horsepower machines. In many cases, the higher horsepowers are achieved by turbocharging the engines, and the higher temperatures and pressures which exist in turbocharged engines have usually resulted in an increase in oxides of nitrogen emissions. Some of the turbocharged engines also use intercoolers between the turbocharger and the intake port to reduce the intake air temperature and thereby increase horsepower.
Many commercial diesel engines utilize a direct injection, valve-in-head-type design, with an open combustion chamber in the piston. Heretofore, when engines of this type have been operated at high output levels, the engines had had poor exhaust emission characteristics, particularly oxides of nitrogen emissions.